TingPing parent
Maintainer refuses to merge bad work, shame on them?
If it was really bad work, then of course not.
The problem is that poor quality isn't the reason why they refuse. While not related to the file picker, I personally offered to port an important part of GTK3 to GTK4 (status icon support) and one of the maintainers told me flat out that he would not merge my work because "it was no longer in line with the direction GNOME is heading".
I suspect the real reason behind their refusal is purely subjective, unfortunately.
That's not subjective. When they merge code like that and then you disappear, they're now stuck budgeting time to maintain that API for years. They can't be expected to do that work when no maintainers care enough and no GNOME apps are even going to use that API (Status icons were removed from the GNOME HIG years ago)
If you don't want to go through the trouble of becoming a committed long-term GTK maintainer yourself just to get this in, why not maintain that particular feature as a separate library?